Small-Molecular Donor Based Efficient Organic Solar Cells with Thermally Stable Morphologies^†

Small-molecular organic solar cells usually exhibited unsatisfactory device stability, which might originate from their molecular diffusion behaviors. Herein, based on the all-small-molecule system HD-1:BTP-eC9, we reported a dimerized acceptor DC9, and its corresponding monomer acceptor eOD. In comparison with eOD, the dimeric acceptor DC9 displayed higher glass transition temperature (T_g) but reduced molecular planarity and crystallinity. The all-small molecule blend utilizing HD-1:eOD demonstrated a power conversion efficiency (PCE) of 15.13%, surpassing the value of 14.10% for the HD-1:DC9 blend. While, incorporating polymer donor PM6 into the HD-1:DC9 blend improved its morphology and charge transport dynamics, resulting in a device efficiency of over 16%, representing the rare case utilizing small-molecular donor and dimeric acceptor with PCE over 16%. Morphological characterization results affirmed that the surface morphologies and molecular packing behaviors of the blend films based on HD-1 were largely retained even after prolonged annealing and aging at 85 °C. Consequently, the PCEs of the blend films based on HD-1:eOD, HD-1:DC9, and HD-1:PM6:DC9 consistently remained over 98% of their initial efficiency after 1000 h of thermal annealing aging at 85 °C. These findings highlight the potential of small-molecular based active layer in the fabrication of efficient and stable OSCs.